The Most Dangerous Path in Britain

Where is the most dangerous path in Britain?  Crib Goch on Snowdon?  Striding Edge on Helvelyn? Or maybe the Cuillin Ridge in Scotland?

If, like me, you are not keen to be clinging on above a near vertical drop, then you would want to rate all of those as pretty hairy.  However, the most dangerous path in Britain is actually as flat as a pancake…

…and therein lies the danger.

Believe it or not, this is a public right of way.  It is actually a byway, which means that you are allowed to drive on it, should you want to.  It is even marked on Google maps – The Broomway.

Rising sea level has made the Essex coast a maze of islands, separated by tidal channels.  Until 1932, The Broomway was the only route to Foulness Island, other than by boat.  There’s a bit of a causeway to get you started but then you are out on the flat mud of Maplin Sands, walking on a compass bearing parallel to the coast.  There are no footprints to follow, with each retreat of the tide leaving a fresh new surface.

Why is it so dangerous?  Well because it is so flat, the tide comes in very fast: faster than you can run.

In the diagram you can see that, for the same increase in water height by the tide, on the gently sloping beach the water comes in and covers a much greater area.  It has got the same amount of time to do this before the tide turns again, so on a gentle slope the water has to flow in very fast.

Not only do you have to get the tide right, but there is the possibility of sea mist, gloopy mud and unexploded devices.  (Maplin Sands is a firing range on weekdays.)

And as sea level continues to gradually rise, the window of opportunity gets ever shorter.

I stayed safely above the high tide mark and left my imagination to explore The Broomway!

Submergent Coastlines

If you hunted for some more rias after last week’s post, you will have discovered that they are mainly on the south coast of England.  This coast is a submergent coastline.  It is becoming submerged as the sea level rises relative to the land.

So why don’t all of Britain’s coasts have rias?  Surely the sea is rising everywhere right?

Yes, it is, by about 20 cm from 1880 to 2009.

But in other parts of Britain the land is rising too.  In the south the land is sinking by about 3 cm per 100 years.

So the sea level is going up and at the same time the land is sinking down.  The possibility of flooding increases year by year.

Along the ria of the River Colne the path was up on a raised bank above the marshland.

There were places where the rising tide could flow through the bank to maintain the wetland on the other side, but the amount getting through could be controlled.

Further up the Colne, at Wivenhoe, a flood barrier has been installed in the river, and embankments stretch onto the land either side.  Lock gates can be closed to prevent excessively high tides flooding Colchester.

 

Photo by Ben Pearson

Flood barriers are being closed more and more frequently as the land in this area continues to sink and the sea continues to rise.  The coastline is becoming more and more artificial, as barriers are built, strengthened and raised to continue to keep out the sea.

At what point should we give up the fight?

It depends on what is being protected.  The more valuable the land and buildings, the more money is likely to be available for building suitable flood defences.  There’s already talk of Thames Barrier 2, further downstream, to secure the future of London.

Rias

This is the estuary of the River Colne, in Essex.

Given the size of the estuary you are perhaps thinking that the river itself is a sizeable torrent but…

…this is the Colne, just about a mile from where it becomes tidal.  So how come the tidal part of the Colne leaves such an impression on the landscape?

The answer is that the Colne is a ria.  A ria is a river valley that has been permanently flooded by the sea.  The sea level has risen allowing it to come inland along the river and spill over onto the flat valley floor on either side.  And it is not just the main valley that is flooded but also the lower tributaries too.

I left the main channel to follow Brightlingsea Creek and then turned off again to follow the smaller St Osyth Creek.

Both the tributary and its tributary were tidal and much, much wider than you would expect from their feeding rivers.

So the rivers formed the valleys and then the sea rose and flooded them.  Thus the sea was lower in the past and, as we saw last week, this is evidence for previously lower temperatures, with water locked up in ice rather than in the sea.

Subscribers check your inbox for some notes to help you spot other British rias.